This invention relates to a spare or auxiliary fuel tank supplementarily disposed to a main fuel tank for containing internal-combustion-engine fuel.
Such spare fuel tanks (hereinafter called spare tank) have traditionally been disposed either as a separate type, outside the main fuel tank (hereinafter called main tank), or as a built-in type, inside the same and integrally constructed therewith. The separate type, the first type developed, is defective in that it must be supplied fuel independently of the main tank and that it must be constantly checked to see if it is empty as it has no connection with the main tank. In some cases it communicates with the main tank, but it must then be more carefully checked for fear of being inadvertently emptied. The latter type appeared as an advanced type, and is widely used today. In one bottom corner of a main tank a certain space is separately occupied, in this type, for a spare tank by means of secluding or separating plates welded to the main tank. This advanced built-in type is apparently very convenient and practical in that it does not need individual or dual supplying of fuel because of automatic and simultaneous fuel supplying to both, and that it dispenses with the communication through piping between both tanks.
This improved device is, however, not free from some disadvantages, such as (1) the difficulty of welding separating plates onto the bottom and side walls of the main tank because of the location thereof; (2) likelihood of fuel leakage at the welded portions due to difficulty of the welding operation. In a normal case wherein the main tank is constructed in a narrow and restricted space, the welding operation is difficult and apt to be defective. Once fuel leakage occurs at the welded portion, the fuel in the spare tank lowers as the fuel in the main tank decreases, by naturally flowing out into the main tank, and the spare tank becomes unable to function as a spare tank. In addition, repairing this spare tank is very difficult because it must be inevitably worked through a comparatively small opening of the main tank. Difficulty in cleaning the spare tank, in assembly and operating time, is another shortcoming of this type; when doing the absolutely necessary work of removing scale, slugs, and spatters after the welding, and when performing the regularly necessitated cleaning work of draining and removing deposits much difficulty in cleaning the inside of the tank is encountered because the tank has no drain.
In most assembly lines two types, i.e., vehicles with and without a spare tank, are required to be assembled parallelly; it is a rather rare case that all the vehicles assembled are installed with a spare tank. It will make the assemblying line very complicated and inconvenient to prepare two types of main tanks in one factory. Especially when the main tank is integrally constructed onto the channel-shaped frame, the frame itself should be manufactured in two different types, which leads to the double inventory of truck body frames with great unfavorable effects.